This invention relates generally to drive mechanisms for imparting oscillating/reciprocating motion to a part in a machine and, more particularly, to an adjustable reciprocating drive mechanism including means for controlling the stroke length of sealing jaws in a form and fill packaging apparatus.
In form and fill packaging apparatus, a continuous web of sheet material is transformed into a tube for packaging weighed or volumetrically controlled charges of product. The tube is separated into individual packages with transverse seals formed below and above the charge to complete the package which is then severed from the continuous tube.
In packaging relatively light and irregularly shaped products, such as potato chips, one such apparatus is disclosed in U.S. Pat. No. 3,668,815 to Henry et al, assigned to the same assignee as the present invention. In that appratus, gripping members engaging the tube are provided to form a temporary seal. The product being packaged is introduced into the open end of the tube. After settling the packaged product, a pair of sealing jaws engage the tube to form a transverse heat seal to fully seal the contents. While engaging the packaging tube, the sealing jaws move in a downward drawing stroke to draw an additional package length of tube for the next packaging cycle. At the bottom of the drawing stroke the sealing jaws are withdrawn for return to the sealing station. The stroke length of the sealing jaws corresponds to the desired package length.
The packaging apparatus of the type disclosed in U.S. Pat. No. 3,668,815 includes a drive mechanism that moves the sealing jaws in reciprocating movement and allows for adjustment in the stroke length to run different sized bags. The drive mechanism basically includes a power lever oscillated by a connecting rod and crank mechanism. An adjustable pitman is attached to the power lever to oscillate pairs of drive levers and connecting arms interconnected to the sealing jaw carriage. The pitman comprises two slidable links and is adjustable to vary the upper limit or home position. The power lever includes an arcuate slot to readjust the stroke length of the sealing jaws.
While this arrangement is effective to allow adjustment of the sealing jaw carriage, it is necessary to stop the packaging machine and interrupt production to make the adjustment. In addition, this arrangement of parts requires an initial adjustment to give a rough estimation of the required stroke length; subsequent adjustments being necessary to properly set the sealing jaws in the final position and to assure the proper stroke.
The oscillating power lever and arm arrangement connecting the pitman to the sealing jaws tends to increase the cost of the apparatus. Close tolerances are required for these parts to properly interconnect the sealing jaws to the drive mechanism to achieve the relatively precisional movement of the sealing jaws, further adding to the cost. Furthermore, the extra weight and the movement of these parts in the same relative direction increases the momentum that must be overcome at the ends of the stroke adding to the power required and increasing the wear of the parts.